All the advice already given is sound
Nothing new on race day (apart from running further than ever before - obviously)
Start further back than you intend to finish - this will help you go off slowly and you'll find it much easier at the end passing people than you willif you have dozens of people passing you as you feel like you're dying. If you're not sure where to stand - ask somebody nearby how long they hope to take and adjust your position accordingly - chatting to people will take your mind off the nerves
Have something in your bag to eat and drink after the race - ideally some protein and carbs but so long as you can stomach it, whatever takes your fancy is fine
Also - give yourself at least an hour longer to get there than you think you'll need. There won't be enough car parking (or at least that's how it will seem as you sit in the queue) or enough toilets - this is a common theme at every race - and the lastt hing you need is to be extra stressed trying to figure out where you're going. If you do get there early, use the time to warm up, wander round the merchandise stalls, go to the toilet at least one more time than you need, seek out other forumites (I guess there's a thread over in Events that you could join in and maybe agree a suitable meeting point) or just sit back and feel thankful that you're not in one of those cars caught up in the ever more frustrated queue.
Above all - enjoy yourself. Don't stress about finishing times, it's a PB whatever happens, just get yourself from the start to the finish the start looking forward to the next one.